The present invention relates to the drilling of well bores, and, more particularly, to the impact assisted drilling of well bores using a rotary bit connected to the end of a drilling string.
In connection with the recovery of hydrocarbons and other minerals from the earth, wells are generally drilled in an earth formation using a variety of different methods and equipment. According to a method often used, a roller cone bit or fixed cutter bit is rotated against the subsurface formation to form the well bore. The bit is rotated in the well bore through the rotation of a drill string attached to the bit and/or by the rotary force imparted to the bit by a subsurface fluid motor powered by the flow of drilling fluid through the drill string.
A problem associated with normal rotary drilling of this type, particularly when a fixed bit configuration is used, is that the bit can drag or stop rotating as a result of encountering a relatively large load in the well bore W while the attached drill string continues to turn. This alone can cause damage, and, even if the torque applied through the string eventually succeeds in breaking the bit free of the formation, the sudden release of the bit can cause it to rotate faster than the drill string. The latter phenomenon can cause problems in the operation of the drilling assembly and in the formation of the well bore but can be eliminated or reduced by reducing the weight-on-bit. However, weight-on-bit reduction may produce undesirable effects such as a reduction in the rate-of-penetration of the bit into the formation.
Therefore, what is need is a drilling system that eliminates the above problems.